Sunday, July 14, 2013

Recovering Nutrients

Last week I blogged on the N-E-W paradigm that considers wastewater treatment plants as resource recovery facilities instead of waste disposal points (like paper and glass recycling centers instead of taking stuff to "the dump"). This week I'll focus on the "N" and think about what nutrients can be recovered and some of the factors influencing nutrient recovery. I've grouped them into the positive "driving forces" and the negative "hurdles" that prevent us from recovering nutrients.

Driving Forces

1. Non-renewable resources

Arguably the #1 reason to consider nutrient recovery - specifically focused on phosphorus, I should say - is that it's an opportunity to recover and reuse a valuable non-renewable resource. There is only a finite amount of phosphorus that can be mined and used for fertilizer. The sources of phosphorus rock that we are currently using are relatively cheap and easy to mine. Estimates for global reserves of phosphorus keep shifting and growing as more reserves are found, but the availability of easy-to-access phosphorus rock will eventually dwindle and fade, forcing us to look for less-accessible phosphorus. My good colleague and mentor Dr. James Barnard notes that at some point in the future we may be so short of rock phosphorus that we'll be mining old landfills for the P that's in sludge and other materials dumped there, so maybe we should start landfilling P-rich sludge residues (e.g. incinerator ash) in locations that will be easier to access in the future... put a big P right here sign over that part of the landfill! Way in the future we'll be dredging rivers and sea beds to glean a few grams of phosphorus, so why don't we look more closely at our current phosphorus balance and grab the P at the wastewater treatment facility where it's relatively easy?

2. Shifting the balance

The case for P recovery is pretty strong based on it being a non-renewable resource that's essential for growing food. It can also be argued that if we're trying to remove P from wastewater to prevent eutrophication, then we might as well recover that phosphorus and make good use of it. In essence, that's what we're doing when we take the "sludge" from a treatment facility and magically change the name to "biosolids" (forgive the thinly veiled sarcasm) and apply it to farm land. Whatever P is captured in the solids, goes back to the land instead of being washed out into the rivers and oceans. So let's shift more of the P into the solids so more of it goes back to the land, right? Unfortunately, the balance of phosphorus to nitrogen in the biosolids from wastewater treatment facilities is non-ideal for most soils and so we end up putting too much P back on the land to get the nitrogen needed.

Global Nitrogen Fluxes

Shifting our focus to nitrogen, we can see that the human impact on the natural nitrogen cycle has skewed the nutrient balance considerably. If we can redress some of that through N recovery and reuse in biosolids or by capturing nitrogen directly at the treatment plant then perhaps we're focused on one of the most important planetary boundaries?

3. Setting an example

If we think about changing attitudes and actions, I think nothing is more powerful than leadership by example. We maybe under-emphasize the need for individuals who will be champions for change. I can think of several people in the wastewater treatment industry that inspire us to look at resource recovery more closely. They have persuaded their organizations to take some bold steps in implementing nutrient recovery. We need more resource recovery champions to help us to see the driving factors more clearly and overcome the hurdles listed below...

Hurdles

1. Money

During some of the training I received on sustainability when I was in Australia, Susanne Cooper taught me that if something isn't financially sustainable then it's not sustainable. This is certainly true. We need to balance the need to protect the environment and human health with the cost of doing it. Conversely, we also need to see the wider benefits - often non-financial - of doing the right thing with resource recovery. We also need to make sure we use the right approach in our financial calculations. In many cases we fall into the trap of trying to justify resource recovery projects over 1 - 5 years of "pay-back" i.e. we force the project to pay for itself, whereas the other activities at the treatment facilities are costs that do not pay for themselves. If we can get a payback, that's great, but let's look at the non-financial benefits too.

2. Focus

There are many other priorities for wastewater treatment facilities: meeting permit, protecting human health, dealing with staffing issues, odour complaints... so its tough to add the new focus of nutrient recovery. That's where the resource recovery champions are key. Almost every professional I know in the wastewater treatment industry wants to "do the right thing" for public health and the environment; in many cases it was the reason why they chose their particular career path (let's face it, there are more glamorous and well-paid jobs!). If we are to make a difference in the global nutrient balance through nutrient recovery, we need our champions to tap into our desire to "do the right thing" for the environment.

3. Knowledge

If we're to tap into nutrients and recover them at our wastewater treatment facilities then we need to know how to do it. WERF has a Knowledge area focused on Resource Recovery which is helping facilitate our understanding of the mechanisms and technologies that can be used in nutrient recovery.

So, in looking at the Driving Forces compelling us to seriously consider nutrient recovery, how do we overcome the Hurdles? I welcome comments and opinions.

About Me

A wastewater engineer since the early 90's, originally from the UK, now living in Kansas with a brief but wonderful interlude in Western Australia. Interested in sustainability, water issues, process modeling and online instrumentation. Also interested in social media and most things vaguely geeky.